Deep-Dive Guides · Lanthanides & Actinides
f-Block — Lanthanides & Actinides deep dive
The f-block is governed by one structural fact with enormous consequences: the valence 4f (lanthanides) and 5f (actinides) orbitals are buried deep inside the ion, shielded by the filled 5s5p (or 6s6p) shells.
Free extract — the opening section of the guide, in full.
0. How to use this guide — the buried-f logic map
One fact explains almost everything about the lanthanides: the 4f electrons are core-like, shielded by the 5s²5p⁶ shell, so they do not participate significantly in bonding and are barely perturbed by ligands. Fix its consequences and the descriptive chemistry follows.
| Consequence of buried 4f | What you observe |
|---|---|
| f-electrons don't bond → oxidation state set by 6s/5d loss | +3 dominates the whole series; ions are hard, ionic, similar |
| f-orbitals shielded → tiny crystal-field splitting (~10² cm⁻¹, ≪ Δ of d-block) | Colours/spectra almost independent of ligand; sharp, line-like f–f bands |
| f-orbital angular momentum not quenched (buried, not felt by ligands) | Magnetic moments follow the Landé g√[J(J+1)], not spin-only |
| Poor shielding of nuclear charge by 4f electrons themselves | Steady size shrink across the series → lanthanide contraction |
| All +3 ions nearly identical, differ only slowly in size | Notoriously hard to separate; separation exploits the small radius difference |
Read the rest of this guide
The remaining 11 sections — Lanthanides: position, configurations, the +3 world, The lanthanide contraction & its consequences, Oxidation states beyond +3, Colour, spectra & magnetism and more — are part of ChemVidya Full Access, along with the other guides, the books, the study notes and 6,000+ practice questions with worked solutions.